In the treatment of waste water in a dissolved air flotation ("DAF") system, the solids are clarified through means of flotation of particles to the surface of the liquid. The flotation of particles to the surface of the liquid has been accomplished in the past through various means of aerating the waste water.
In a typical dissolved air flotation system, recycled water or the raw waste water is pressurized. Compressed air is added to the pressurization tank. This water, along with flocculating chemicals is introduced into the DAF vessel. Bubbles are formed as the air entrained in the water is released from pressure. The particles attach themselves to or become trapped by the bubbles. As the bubbles rise to the surface of the water, the particles are carried along. When the bubbles reach the surface the air escapes, forming a foam or sludge layer on the surface. The sludge layer contains the particles deposited by the escaping air bubbles. The sludge layer is kept intact and skimmed from the vessel to be processed by various means. Thus, through aeration, the waste water is fed needed air and chemicals and the water clarified.
Presently available methods and apparatus for aerating waste water in a DAF treatment system have failed to efficiently entrain sufficient amounts of air in the waste water necessary to obtain maximum particle flotation without substantial use of chemicals. Additionally, aeration of waste water using prior art methods and apparatus has further resulted in excess movement or circulation of the treated waste water, damaging the sludge layer formed.